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benanderson89

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  1. I'll give that a bash sometime today! Thankfully I already have some compatible opto chips in the garage so I can just fish those out.
  2. Hello again everyone! My Macintosh Classic is still being a pain in the backside. Today I replaced DP 3, 4 and 6 (though I've not done the opto isolator yet), and I'm still having issues. Screen shaking and taking a long time to reach a bootable voltage as per this thread from early October still apply. However, after replacing those three diodes it's somehow even worse! Not only do I still have screen shaking issues, it took a solid two and a half minutes to reach a bootable voltage (although it has been switched off for nearly a month) -- though unlike before the screen never stabilise
  3. Do you know the part numbers for DP3 and DP4? I may as well buy all the parts. I have two new optos in a baggy in the garage so I may as well buy all the diodes and just replace everything in one shot if I have to spend the time setting everything up anyway.
  4. You know, I think I meant to replace that and never got around to it (partly because I couldn't find it since it's one of the small ones). I'll open the case tomorrow and test the diode. EDIT: Wait, no, the giant one with the heat sink. Why did I think one of the little ones? Yes, there was a lot of gunk around that area of the board and it'll absolutely be that diode I forgot to replace. I'll remind myself to order a part tomorrow.
  5. The Macintosh Classic I've been working on is now done. All the large electrolytic caps on the analogue board and the caps on the logic board were all replaced. Voltages measure stable and within spec from the floppy disk port. C2 on the CRT neck board was also replaced. However I've noticed that when the computer is left switched off for a long period of time, the voltage readings are very low, the screen is the wrong shape, it shakes violently and there's a chequerboard pattern. If you wait, the voltage eventually creeps up and it boots (but the memory check takes a while), wait
  6. It doesn't, but there he is, churning away.
  7. Back from the repair shop! IT'S ALIIIIVE! Pins 1 and 5 are supposed to be together. 1 is G1 and 5 is ground of G1. A lad from the vintage television forums said that's what it's for. My actual issue was that two caps, the only two I didn't replace that were hidden under a massive gob of hot glue, had went open circuit. So there was a floating voltage to ground and no current to drive the CRT. End result is that the power supply protection circuitry kicked in. I still have a "shimmering" issue with the display after it's had a chance to warm up, so I think there's one more old
  8. Theres no short to ground in the brightness circuit so we can rule that out. The short is the tube itself.
  9. There's no shorts anywhere when the CRT is disconnected.
  10. The rest of the computer is fine - it's only the when the tube is connected that the low voltage side shorts. The short is on the pins of the CRT itself.
  11. 1MB is installed on the motherboard since the Classic is basically a Macintosh Plus. This is what the screen scan in question looked like. It wasn't slow enough to see it draw; it was so quick I'm sure anyone with epilepsy would go into a fit. After switching off the machine and switching it back on, nothing happens. I've not ran tests on the tube inside my Classic since that's off in storage, but I've tested the tube I've had delivered. It's definitely not a heater short as the filament glows and everything holds nice and stable. No continuity or resistance between either th
  12. This is the second tube I have that just got delivered from eBay, so yeah it needs a bit of a clean and pin 1 bent back into place.
  13. Looking at the neck of the tube, are you ABSOLUTELY SURE pins one and five are supposed to NOT have continuity? They look like one solid piece of metal from here (pins covered with blue and pink plastic commoned an outer sleeve around the cathode) I have a funny feeling I'm chasing yet another red herring (since I was told no pins except 3/4, the filament, should have continuity) and both my tubes are absolutely fine. Even so, I've used my little bench supply to test the heater filament and it holds nice and steady. Likewise I've blasted pins one and five with everythin
  14. Asked ye-olde reddit electronics sub for help. Old TV repair guy says he's confident it's a GK short. From what I can tell you basically just discharge a whacking huge capacitor between the two pins and it vaporises the debris off of the gun. Wondering how I could do that with what I have.
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